1. Field of the Invention
The present invention generally relates to power supply control device and, more particularly, to a power supply control device for supplying an electric current to a heating element or a part requiring power supply and a heating device and a fixing device to which an electric current is supplied by the power supply control device.
2. Description of the Related Art
An image forming apparatus represented by a copy machine, a printer, a facsimile, a combination machine of the aforementioned or the like forms an image by image forming part and transfers the formed image onto a sheet-like recording material such as a recording paper or an OHP sheet. Various recording methods are materialized as an image recording method used in the image forming apparatus. From among those methods, an electrophotographic method is used widely by the above-mentioned apparatuses from viewpoints of high-speed, high image quality and low cost.
It is common to use a fixing device to fix an unfixed toner image transferred on a recording material by heat and pressure. A heat-roller method is used in many cases at present time as a fixing method in a fixing device from viewpoints of high-speed and safety. The heat-roller method is a method to heat a recording material, which is a material to be heated when viewing from a heating member, by passing through the recording material between the heating member such as a heating roller, which is heated by the heating member such as a halogen heater, and an opposing rotational member, which is arranged opposite to the heating member so as to form a mutual pressure-contacting part referred to as a pressure-contacting nip part by being brought into pressure-contact with the heating member. A metal roller, in which iron or aluminum is used as a metal core, is mainly used in the heating member, thereby increasing a heat capacity thereof. Thus, there is needed a long start-up time such as several minutes to ten and several minutes so as to raise a temperature to about 180° C., which is a temperature (fixing temperature) at which a toner is melted and usable.
Then, in the image forming apparatus, an electric power is supplied to a heat-generating member provided in the heating member also during a standby period in which a user of the apparatus does not perform printing, so as to maintain the temperature at a pre-heating temperature slightly lower than a usable temperature (fixing temperature). Thereby, the temperature of the heating roller is raised immediately to the usable temperature (fixing roller).
When an importance is given to the start-up of the temperature, a power which is not necessary for image formation, that is, a waste electric power, is consumed by the heat-generating member as a standby power during a period when the apparatus is not used. There is a result of investigation that indicates that energy consumed at the standby period occupies about 70 to 80 percent of energy consumed by an image forming apparatus.
In recent years, energy-saving regulation has been enacted due to the rise in environmental protection consciousness in each country. The Law concerning energy saving has been revised and strengthened in Japan, and an energy saving program such as the Energy Star or the ZESM (Zero Energy Star Mode) has been enacted also in the U.S. When attempting energy saving so as to respond to those regulations and programs, it is desired for image forming apparatuses to obtain a large energy saving effect in reducing energy consumption during a standby period to reduce a power supply to close to zero during the standby period.
When setting the power during the standby period of the apparatus to zero while the conventional structure of a fixing device is unchanged, a time is spent on rising of the temperature of the heat roller when restarting the device. Thus, the standby period is increased and use convenience is deteriorated. Accordingly, a structure of rapidly raising the heat roller is required in realizing energy saving in an image forming apparatus. For example, the above-mentioned ZESM requires an extremely severe condition such that a restart-up time from the standby state be less than 10 seconds.
In order to shorten the temperature rising time, it is possible to reduce the heat capacity of the heating member or to increase a supply power to the heating member (heat-generating member). With regard to making a low heat capacity, a startup with a short time such as 10 to 30 seconds in a middle and low print speed range such as about 50 cpm (50 sheets/1 minute) by reducing a thickness of a heat roller or a fixing roller as the heating means to several mm to 1 mm or using a film or a belt member as the heating member, thereby enabling reduction in the temperature rising time.
Although a supply voltage may be raised to increase a supply power to the heating means, a commercial power supply of 100V/15 A is general in a normal office in Japan, and 1500 W is an upper limit of the supply power. Thus, it is difficult to increase a supply power to the heating means by a general commercial power supply alone.
Although the low heat capacity of the heating means is effective in the middle and low print speed range, it is difficult to maintain the temperature of the heating means at a predetermined temperature is the heat capacity of the heating member is small since an amount of heat taken by a recording material from the heating means is larger than an amount of heat given to the heating means as a number of recording materials supplied per unit time is large in a high speed print range higher than 60 cpm (60 sheets/1 minute). In an image forming apparatus, such a decrease in the heating means may cause a fixation failure.
In order to solve the above-mentioned problem, there is suggested an image forming apparatus, which uses a power supply voltage of 200V to achieve a high speed range of a print speed. However, it is necessary to change a power supply source at an installation location, and, thus, it is not a general solution. Additionally, there is an apparatus put into practice that used two lines of 100V/15 A to increase a total supply power, but it is difficult to install the apparatus unless receptacles of two separate lines are provided close to the installation location. Thus, conventionally, it is difficult to increase the upper limit of the supply power so as to raise the temperature of the heat roller (heating means) in a short time.
In the above-mentioned circumstance, as a method of realizing prevention of the temperature decrease of the fixing device by increasing a maximum supply power, there is suggested an image forming apparatus having a rechargeable auxiliary power supply device, which is different from the commercial power supply (100V/15 A). For example, in the following Patent Document 1, a plurality of heaters are provided to heating means as a heat-generating member as shown in FIG. 1, and an electric power is supplied to one of the heating members from a commercial power source line, which serves as a main power supply device, and an electric power is supplied from an auxiliary power supply device to the other heating member so as to increase a maximum supply power to the heating means to achieve a reduction in the standup time and prevent a temperature decrease. As the auxiliary power supply source, there is typically a secondary battery such as a lead battery or a nickel-cadmium battery. However, the secondary battery deteriorates and the capacity thereof is reduced while repeating charge and discharge, and a service life is shortened as a discharge is carried out with a large current.
Even the nickel-cadmium battery, which is generally considered to have a long service life with a large current, a number of repetitions of charge and discharge is about 500 to 1000 times. For example, if charge and discharge are repeated for twenty timed per one day, the service life will expire after use of about one month. This requires labor of replacing the battery, and a running cost such as a battery cost is very high. Further, from viewpoint of a charge time, since it requires a long time to charge a large-capacity battery, such a battery cannot be used for an application in which charge and discharge are repeated in a day. Thus, it is difficult in practice to use the secondary battery. As mentioned above, since there are problems in use of a secondary battery in practice, the Patent Document 1 also discloses use of a capacitor having a large capacity such as an electric double layer capacitor.
The large-capacity capacitor has the following advantages as compared to a battery. First, a number of repetitions is more than several million times, which is almost no limitation, and there is little deterioration of the charge characteristic and a periodic maintenance is not needed. Second, the charge time can be set to several seconds to several tens seconds while that of the secondary battery is several hours. Additionally, the electric double layer capacitor is capable of flowing a large current such as several tens amperes to million amperes, which enables a large power supply in a short time.
As another method of using the auxiliary power supply device, there is a method disclosed in the following Patent Document 2. In the Patent Document 2, as shown in FIG. 2, a power supply device, which supplied DC 5V or 24V to an image forming apparatus from the commercial power source line (100V/15 A), and a charge device, which supplies an electric power from a rechargeable battery as an auxiliary power supply device, are provided to supply a power from the both to a main control part so as to reduce a load to the power supply device by an amount corresponding to the power supplied by the rechargeable battery, which achieves a reduction in a maximum power supply of the power supply device.
Patent Document 1: Japanese Laid-Open Patent Application No. 2003-140484
Patent Document 2: Japanese Laid-Open Patent Application No. 2002-044305
According to the method of supplying an electric power to the auxiliary heater such as disclosed in the Patent Document 1, the auxiliary heater is needed in addition to the main heater as a heat-generating member of the heating means, and, thus, there is a limitation in reduction of a size of the heating means. Additionally, as shown in FIG. 3, since a large electric power (for example, 1900 W), which is a sum of a maximum power (for example, 1200 W) of the main heater serving as a main heat-generating part and a maximum power (for example, 700 W) of the auxiliary heater, can be supplied to the heat-generating member, it is considered that an excessive temperature rise is invited when the apparatus runs out of control in the case of the heating means having a structure in which a heat capacitance is decreased in consideration of a startup characteristic.
In the Patent Document 2, in order to always supply electric power during an image forming operation using a battery with a sufficient margin in a charge current, a sufficiently large charge current is needed. Thus, it is difficult to use a charge device having a relatively small capacity such as an electric double layer capacitor, and a charge device which cannot acquire a sufficient capacity such as a capacitor cannot be used as an auxiliary power supply device. Additionally, it is difficult to miniaturize the charge device by reducing the charge current to the battery. Thus, it is not suitable for an application of an image forming apparatus of a short time temperature raise or a high-speed print. Additionally, if the image forming apparatus is equipped with a device such as a hard disk drive or a stapler, which requires a large electric power instantaneously from an auxiliary power supply device, it is difficult to increase an electric current supplied to the heating means. Thus, it is not suitable for an application to an image forming apparatus of a short time temperature raise or a high-speed print.
Moreover, although a system can be achieved within a limited electric power of a commercial power supply line by supplying a required electric power from an auxiliary power supply even in a case where a large electric power is required instantaneously for operating a hard disk drive (HDD) or a stapler such as shown in FIG. 4, it is difficult to increase an amount of power supply to the fixing device in such an application to supply an auxiliary electric power to a specific device, and the short time temperature raise or a high-speed print cannot be achieved.